This invention relates to steering of wheeled or tracked vehicles and, in particular, to insuring that each of the wheels or tracks are steered about a common center when it is desired to turn the vehicle.
The conventional method of steering the ground engagement means, which may be the tracks or wheels of a vehicle, over different radii, but where the radii have a common center or intersection point, is to use tie rods interconnecting the wheels or tracks of the vehicle. However, there are many types of vehicles which do not permit the use of mechanical linkages for making these adjustments. For example, gantry cranes are built with a clearance between the wheels upon which the crane is propelled so that the crane may bridge the articles which it is transporting. Tie rods would interfere with the operation of the crane insofar as they would make it impossible for the crane to move over these articles. The present invention is particularly useful, therefore, on those vehicles where tie rods are inappropriate to the proper functioning or utilization of the vehicle. Moreover, the present invention allows a much more flexible arrangement for providing the tie rod function without using the mechanical tie rods which are subject to the normal difficulties associated with mechanical arrangements.
The prior art has sought various systems to solve the problem of eliminating tie rods yet retaining the tie rod function. Various mechanical arrangements, other than tie rods, have been devised for insuring that the wheels on opposite sides of a vehicle will turn about a common center but these systems suffer the same mechanical failure problems of the tie rod systems. Other systems rely upon complex diode and resistance bridges for approximating the desired turning radii for the wheels or tracks of the vehicle but these systems are merely approximations and do not accurately reflect the optimum turning radius for each of the wheels or tracks. Still other systems rely upon complex cam arrangements wherein a separate cam is devoted to each wheel or track of the vehicle to be steered and is profiled to insure that the associated wheel turns with the proper radius regardless of the direction or to the degree to which the vehicle is turned. These cam type arrangements are mechanical in nature insofar as a cam follower must sense the surface of the cam resulting in wearing of the follower and friction between the follower and the cam. The present invention eliminates these disadvantages while providing an effective and reliable steering control.